On the Physiology of the Sensory-Collapse Test.

The sensory-collapse test (formerly the scratch-collapse test) is a physical examination finding describing a momentary inhibition of external shoulder rotation following light stimulation of an injured nerve in the ipsilateral limb. Similar to other physical examination tests designed to interrogate nerve compression, such as the Phalen or Tinel tests, its test characteristics demonstrate variation. There remains speculation about the test's existence and anatomic basis. The literature of mammalian reflex physiology was reviewed with an emphasis on the sensory pathways from the upper extremity, the extrapyramidal system, and newly discovered pathways and concepts of nociception. A clear reflex pathway is described connecting the stimulus within an injured nerve through the afferent pathways in the fasciculus cuneatus in the spinal cord directly to the lateral reticulospinal tract, resulting in the inhibition of extensor muscles in the proximal limb (eg, shoulder) and activation of the limb flexors by acting upon alpha and gamma motor neurons. The sensory-collapse test represents a reflex pathway that teleologically provides a mechanism to protect an injured nerve by withdrawal toward the trunk and away from the noxious environment.

Investigation of the Neuro-Regenerative Effects of Bioresonance and Magnetotherapy in Sciatic Nerve Damage-Induced Rats / Investigación de los Efectos Neurorregenerativos de Biorresonancia y Magnetoterapia en Ratas Inducidas por Daño del Nervio Ciático

SUMMARY: Peripheral nerve damage is a significant clinical problem that can lead to severe complications in patients. Regarding the regeneration of peripheral nerves, it is crucial to use experimental animals' nerves and use different evaluation methods. Epineural or perineural suturing is the gold standard in treating sciatic nerve injury, but nerve repair is often unsuccessful. This study aimed to investigate the neuroregenerative effects of magnetotherapy and bioresonance in experimental animals with sciatic nerve damage. In this study, 24 female Wistar rats were divided into 7 groups (n=6) as follows: Group 1 (Control), Group 2 (Axonotmesis control), Group 3 (Anastomosis control), Group 4 (Axonotmesis + magnetotherapy), Group 5 (Anastomosis + magnetotherapy), Group 6 (Axonotmesis + bioresonance), Group 7 (Anastomosis + bioresonance). Magnetotherapy and bioresonance treatments were applied for 12 weeks. Behavioural tests and EMG tests were performed at the end of the 12th week. Then the rats were sacrificed, and a histopathological evaluation was made. The statistical significance level was taken as 5 % in the calculations, and the SPSS (IBM SPSS for Windows, ver.21) statistical package program was used for the calculations. Statistically significant results were obtained in animal behaviour tests, EMG, and pathology groups treated with magnetotherapy. There was no statistically significant difference in the groups treated with bioresonance treatment compared to the control groups. Muscle activity and nerve repair occurred in experimental animals with acute peripheral nerve damage due to 12 weeks of magnetotherapy, and further studies should support these results.

El daño a los nervios periféricos es un problema clínico importante que puede conducir a complicaciones graves en los pacientes. En cuanto a la regeneración de los nervios periféricos, es crucial utilizar los nervios de los animales de experimentación y diferentes métodos de evaluación. La sutura epineural o perineural es el gold estándar en el tratamiento de lesiones del nervio ciático, pero la reparación del nervio a menudo no tiene éxito. Este estudio tuvo como objetivo investigar los efectos neuroregenerativos de la magnetoterapia y la biorresonancia en animales de experimentación con daño del nervio ciático. En el estudio, 24 ratas hembras Wistar se dividieron en 7 grupos (n=6) de la siguiente manera: Grupo 1 (Control), Grupo 2 (Control de axonotmesis), Grupo 3 (Control de anastomosis), Grupo 4 (Axonotmesis + magnetoterapia), Grupo 5 (Anastomosis + magnetoterapia), Grupo 6 (Axonotmesis + biorresonancia), Grupo 7 (Anastomosis + biorresonancia). Se aplicaron durante 12 semanas tratamientos de magnetoterapia y biorresonancia. Las pruebas de comportamiento y las pruebas de EMG se realizaron al final de la semana 12. Luego se sacrificaron las ratas y se realizó una evaluación histopatológica. El nivel de significación estadística se tomó como 5 % en los cálculos, y se utilizó el programa de paquete estadístico SPSS (IBM SPSS para Windows, ver.21). Se obtuvieron resultados estadísticamente significativos en pruebas de comportamiento animal, EMG y grupos de patología tratados con magnetoterapia. No hubo diferencia estadísticamente significativa en los grupos con tratamiento de biorresonancia en comparación con los grupos controles. La actividad muscular y la reparación nerviosa, se produjeron en animales de experimentación con daño nervioso periférico agudo, debido a 12 semanas de magnetoterapia.Estudios adicionales deberían respaldar estos resultados.

Retrograde labeling correlates with motor unit number estimation in rapid-stretch nerve injury.

INTRODUCTION/AIMS: Rapid-stretch nerve injuries represent a substantial treatment challenge. No study has examined motor neuron connection after rapid-stretch injury. Our objective in this study was to characterize the electrophysiological properties of graded rapid-stretch nerve injury and assess motor neuron health using retrograde labeling and muscle adenosine triphosphatase (ATPase) histology. METHODS: Male C57BL/6 mice (n = 6 per group) were rapid-stretch injured at four levels of severity: sham injury, stretch within elastic modulus, inelastic deformation, and stretch rupture. Serial compound muscle action potential (CMAP) and motor unit number estimation (MUNE) measurements were made for 48 days, followed by retrograde labeling and muscle ATPase histology. RESULTS: Elastic injuries showed no durable abnormalities. Inelastic injury demonstrated profound initial reduction in CMAP and MUNE (P < .036) on day 2, with partial recovery by day 14 after injury (CMAP: 40% baseline, P = .003; MUNE: 55% baseline, P = .033). However, at the experimental endpoint, CMAP had recovered to baseline with only limited improvement in MUNE. Inelastic injury led to reduced retrograde-labeled neurons and grouped fiber type histology. Rupture injury had severe and nonrecovering electrophysiological impairment, dramatically reducing labeled neurons (P = .005), and atrophic or type 1 muscle fibers. There was an excellent correlation between MUNE and retrograde-labeled tibial motor neurons across injury severities (R2  = 0.96). DISCUSSION: There was no significant electrophysiological derangement in low-severity injuries but there was recoverable conduction block in inelastic injury with slow recovery, potentially due to collateral sprouting. Rupture injuries yielded permanent failure of injured axons to reinnervate. These results provide insight into the pathophysiology of clinical injuries and recovery.

A nerve conduit filled with Wnt5a-loaded fibrin hydrogels promotes peripheral nerve regeneration.

AIMS: Peripheral nerve injury is a significant clinical problem with a substantial impact on quality of life, for which no optimal treatment has been found. This study aimed to analyze the effect and mechanism of Wnt5a-loaded fibrin hydrogel on a 10-mm rat sciatic nerve defect. METHODS: The Wnt5a-loaded fibrin hydrogel was synthesized by mixing a Wnt5a solution with thrombin and fibrinogen solutions. The loading capacity and release profile of Wnt5a-loaded fibrin hydrogel and the effect of Wnt5a on Schwann cells were evaluated in vitro. We also assessed the in vivo repair status via histological analysis of the regenerative nerve and gastrocnemius muscle, electrophysiological examination, gait analysis, and muscle wet weight. RESULTS: We developed a nerve conduit filled with Wnt5a-loaded fibrin hydrogel (Fn) as a sustained-release system to repair a 10-mm rat sciatic nerve defect. In vitro, Wnt5a could promote SC proliferation and the gene expression of vascular endothelial growth factor (VEGF), nerve growth factor (NGF), and cholinergic neurotrophic factor (CNTF), as well as the protein secretion of VEGF and NGF. In vivo, the Wnt5a/Fn group was superior to the hollow, fibrin hydrogel, and Wnt5a groups in terms of axonal growth, myelination, electrophysiological recovery, target organ innervation, and motor function recovery 12 weeks after the operation. CONCLUSION: The Wnt5a/Fn nerve conduit can promote peripheral nerve defect regeneration, with potential clinical applications. The mechanism for this may be the facilitation of multiple neurotrophin secretion, combining vascularization and neurotrophic growth cues.

Sigma-1 receptor increases intracellular calcium in cultured astrocytes and contributes to mechanical allodynia in a model of neuropathic pain.

Recent studies have revealed that glial sigma-1 receptor (Sig-1R) in the spinal cord may be a critical factor to mediate sensory function. However, the functional role of Sig-1R in astrocyte has not been clearly elucidated. Here, we determined whether Sig-1Rs modulate calcium responses in primary cultured astrocytes and pathological changes in spinal astrocytes, and whether they contribute to pain hypersensitivity in naïve mice and neuropathic pain following chronic constriction injury (CCI) of the sciatic nerve in mice. Sig-1R was expressed in glial fibrillary acidic protein (GFAP)-positive cultured astrocytes. Treatment with the Sig-1R agonist, PRE-084 or neurosteroid dehydroepiandrosterone (DHEA) increased intracellular calcium responses in cultured astrocytes, and this increase was blocked by the pretreatment with the Sig-1R antagonist, BD-1047 or neurosteroid progesterone. Intrathecal administration of PRE-084 or DHEA for 10 days induced mechanical and thermal hypersensitivity and increased the number of Sig-1R-immunostained GFAP-positive cells in the superficial dorsal horn (SDH) region of the spinal cord in naïve mice, and these changes were inhibited by administration with BD-1047 or progesterone. In CCI mice, intrathecal administration of BD-1047 or progesterone at post-operative day 14 suppressed the developed mechanical allodynia and the number of Sig-1R-immunostained GFAP-positive cells that were increased in the SDH region of the spinal cord following CCI of the sciatic nerve. These results demonstrate that Sig-1Rs play an important role in the modulation of intracellular calcium responses in cultured astrocytes and pathological changes in spinal astrocytes and that administration of BD-1047 or progesterone alleviates the Sig-1R-induced pain hypersensitivity and the peripheral nerve injury-induced mechanical allodynia.

ZNF382 controls mouse neuropathic pain via silencer-based epigenetic inhibition of Cxcl13 in DRG neurons.

Nerve injury-induced changes of gene expression in dorsal root ganglion (DRG) are critical for neuropathic pain genesis. However, how these changes occur remains elusive. Here we report the down-regulation of zinc finger protein 382 (ZNF382) in injured DRG neurons after nerve injury. Rescuing this down-regulation attenuates nociceptive hypersensitivity. Conversely, mimicking this down-regulation produces neuropathic pain symptoms, which are alleviated by C-X-C motif chemokine 13 (CXCL13) knockdown or its receptor CXCR5 knockout. Mechanistically, an identified cis-acting silencer at distal upstream of the Cxcl13 promoter suppresses Cxcl13 transcription via binding to ZNF382. Blocking this binding or genetically deleting this silencer abolishes the ZNF382 suppression on Cxcl13 transcription and impairs ZNF382-induced antinociception. Moreover, ZNF382 down-regulation disrupts the repressive epigenetic complex containing histone deacetylase 1 and SET domain bifurcated 1 at the silencer-promoter loop, resulting in Cxcl13 transcriptional activation. Thus, ZNF382 down-regulation is required for neuropathic pain likely through silencer-based epigenetic disinhibition of CXCL13, a key neuropathic pain player, in DRG neurons.

Brief Electrical Stimulation Accelerates Axon Regeneration and Promotes Recovery Following Nerve Transection and Repair in Mice.

BACKGROUND: Clinical outcomes following nerve injury repair can be inadequate. Pulsed-current electrical stimulation (ES) is a therapeutic method that facilitates functional recovery by accelerating axon regeneration. However, current clinical ES protocols involve the application of ES for 60 minutes during surgery, which can increase operative complexity and time. Shorter ES protocols could be a strategy to facilitate broader clinical adoption. The purpose of the present study was to determine if a 10-minute ES protocol could improve outcomes. METHODS: C57BL/6J mice were randomized to 3 groups: no ES, 10 minutes of ES, and 60 minutes of ES. In all groups, the sciatic nerve was transected and repaired, and, in the latter 2 groups, ES was applied after repair. Postoperatively, changes to gene expression from dorsal root ganglia were measured after 24 hours. The number of motoneurons regenerating axons was determined by retrograde labeling at 7 days. Histomorphological analyses of the nerve were performed at 14 days. Function was evaluated serially with use of behavioral tests up to 56 days postoperatively, and relative muscle weight was evaluated. RESULTS: Compared with the no-ES group, both ES groups demonstrated increased regeneration-associated gene expression within dorsal root ganglia. The 10-minute and 60-minute ES groups demonstrated accelerated axon regeneration compared with the no-ES group based on increased numbers of labeled motoneurons regenerating axons (mean difference, 202.0 [95% confidence interval (CI), 17.5 to 386.5] and 219.4 [95% CI, 34.9 to 403.9], respectively) and myelinated axon counts (mean difference, 559.3 [95% CI, 241.1 to 877.5] and 339.4 [95% CI, 21.2 to 657.6], respectively). The 10-minute and 60-minute ES groups had improved behavioral recovery, including on grid-walking analysis, compared with the no-ES group (mean difference, 11.9% [95% CI, 3.8% to 20.0%] and 10.9% [95% CI, 2.9% to 19.0%], respectively). There was no difference between the ES groups in measured outcomes. CONCLUSIONS: A 10-minute ES protocol accelerated axon regeneration and facilitated functional recovery. CLINICAL RELEVANCE: The brief (10-minute) ES protocol provided similar benefits to the 60-minute protocol in an acute sciatic nerve transection/repair mice model and merits further studies.

Electrophysiological and anatomical characterization of synaptic remodeling in the mouse whisker thalamus.

In the central nervous system, developmental and pathophysiologic conditions cause a large-scale reorganization of functional connectivity of neural circuits. Here, by using a mouse model for peripheral sensory nerve injury, we present a protocol for combined electrophysiological and anatomical techniques to identify neural basis of synaptic remodeling in the mouse whisker thalamus. Our protocol provides comprehensive approaches to analyze both structural and functional components of synaptic remodeling. For complete details on the use and execution of this protocol, please refer to Ueta and Miyata, (2021).

C-terminal domain small phosphatase 1 (CTDSP1) regulates growth factor expression and axonal regeneration in peripheral nerve tissue.

Peripheral Nerve Injury (PNI) represents a major clinical and economic burden. Despite the ability of peripheral neurons to regenerate their axons after an injury, patients are often left with motor and/or sensory disability and may develop chronic pain. Successful regeneration and target organ reinnervation require comprehensive transcriptional changes in both injured neurons and support cells located at the site of injury. The expression of most of the genes required for axon growth and guidance and for synapsis formation is repressed by a single master transcriptional regulator, the Repressor Element 1 Silencing Transcription factor (REST). Sustained increase of REST levels after injury inhibits axon regeneration and leads to chronic pain. As targeting of transcription factors is challenging, we tested whether modulation of REST activity could be achieved through knockdown of carboxy-terminal domain small phosphatase 1 (CTDSP1), the enzyme that stabilizes REST by preventing its targeting to the proteasome. To test whether knockdown of CTDSP1 promotes neurotrophic factor expression in both support cells located at the site of injury and in peripheral neurons, we transfected mesenchymal progenitor cells (MPCs), a type of support cells that are present at high concentrations at the site of injury, and dorsal root ganglion (DRG) neurons with REST or CTDSP1 specific siRNA. We quantified neurotrophic factor expression by RT-qPCR and Western blot, and brain-derived neurotrophic factor (BDNF) release in the cell culture medium by ELISA, and we measured neurite outgrowth of DRG neurons in culture. Our results show that CTDSP1 knockdown promotes neurotrophic factor expression in both DRG neurons and the support cells MPCs, and promotes DRG neuron regeneration. Therapeutics targeting CTDSP1 activity may, therefore, represent a novel epigenetic strategy to promote peripheral nerve regeneration after PNI by promoting the regenerative program repressed by injury-induced increased levels of REST in both neurons and support cells.

Bioluminescent Optogenetics: A Novel Experimental Therapy to Promote Axon Regeneration after Peripheral Nerve Injury.

Functional recovery after peripheral nerve injury (PNI) is poor, mainly due to the slow and incomplete regeneration of injured axons. Experimental therapies that increase the excitability of the injured axons have proven remarkably successful in promoting regeneration, but their clinical applicability has been limited. Bioluminescent optogenetics (BL-OG) uses luminopsins, fusion proteins of light-generating luciferase and light-sensing ion channels that could be used to increase neuronal excitability if exposed to a suitable substrate. Excitatory luminopsins were expressed in motoneurons of transgenic mice and in wildtype mice transduced with adeno-associated viral vectors. Intraperitoneal administration of coelenterazine (CTZ), a known luciferase substrate, generated intense bioluminescence in peripheral axons. This bioluminescence increased motoneuron excitability. A single administration of CTZ immediately after sciatic nerve transection and repair markedly enhanced motor axon regeneration. Compound muscle action potentials were 3-4 times larger than controls by 4 weeks after injury. The results observed with transgenic mice were comparable to those of mice in which the luminopsin was expressed using viral vectors. Significantly more motoneurons had successfully reinnervated muscle targets four weeks after nerve injury in BL-OG treated mice than in controls. Bioluminescent optogenetics is a promising therapeutic approach to enhancing axon regeneration after PNI.

Determining the real site of peroneal nerve injury with knee dislocation: Earlierier is easier.

Common peroneal nerve (CPN) injury is a recognised complication of traumatic knee dislocation with a direct association between the degree of ligamentous injury and the degree of CPN injury. It is essential explore and repair these injuries in good time to reduce morbidity. Often exploration only involves the portion of this nerve associated with the joint as it courses around the fibular head. However, a recent case highlighted the importance of proximal exploration to its branching point from the sciatic nerve, a known point of fragility, even if other defects have been identified.

Contribution of dorsal horn CGRP-expressing interneurons to mechanical sensitivity.

Primary sensory neurons are generally considered the only source of dorsal horn calcitonin gene-related peptide (CGRP), a neuropeptide critical to the transmission of pain messages. Using a tamoxifen-inducible CalcaCreER transgenic mouse, here we identified a distinct population of CGRP-expressing excitatory interneurons in lamina III of the spinal cord dorsal horn and trigeminal nucleus caudalis. These interneurons have spine-laden, dorsally directed, dendrites, and ventrally directed axons. As under resting conditions, CGRP interneurons are under tonic inhibitory control, neither innocuous nor noxious stimulation provoked significant Fos expression in these neurons. However, synchronous, electrical non-nociceptive Aß primary afferent stimulation of dorsal roots depolarized the CGRP interneurons, consistent with their receipt of a VGLUT1 innervation. On the other hand, chemogenetic activation of the neurons produced a mechanical hypersensitivity in response to von Frey stimulation, whereas their caspase-mediated ablation led to mechanical hyposensitivity. Finally, after partial peripheral nerve injury, innocuous stimulation (brush) induced significant Fos expression in the CGRP interneurons. These findings suggest that CGRP interneurons become hyperexcitable and contribute either to ascending circuits originating in deep dorsal horn or to the reflex circuits in baseline conditions, but not in the setting of nerve injury.

The ability to sense pain is critical to our survival. Normally, pain is provoked by intense heat or cold temperatures, strong force or a chemical stimulus, for example, capsaicin, the pain-provoking substance in chili peppers. However, if nerve fibers in the arms or legs are damaged, pain can occur in response to touch or pressure stimuli that are normally painless. This hypersensitivity is called mechanical allodynia. A protein called calcitonin gene-related peptide, or CGRP, has been implicated in mechanical allodynia and other chronic pain conditions, such as migraine. CGRP is found in, and released from, the neurons that receive and transmit pain messages from tissues, such as skin and muscles, to the spinal cord. However, only a few distinct groups of CGRP-expressing neurons have been identified and it is unclear if these nerve cells also contribute to mechanical allodynia. To investigate this, Löken et al. genetically engineered mice so that all nerve cells containing CGRP produced red fluorescent light when illuminated with a laser. This included a previously unexplored group of CGRP-expressing neurons found in a part of the spinal cord that is known to receive information about non-painful stimuli. Using neuroanatomical methods, Löken et al. monitored the activity of these neurons in response to various stimuli, before and after a partial nerve injury. This partial injury was induced via a surgery that cut off a few, but not all, branches of a key leg nerve. The experiments showed that in their normal state, the CGRP-expressing neurons hardly responded to mechanical stimulation. In fact, it was difficult to establish what they normally respond to. However, after a nerve injury, brushing the mice's skin evoked significant activity in these cells. Moreover, when these CGRP cells were artificially stimulated, the stimulation induced hypersensitivity to mechanical stimuli, even when the mice had no nerve damage. These results suggest that this group of neurons, which are normally suppressed, can become hyperexcitable and contribute to the development of mechanical allodynia. In summary, Löken et al. have identified a group of nerve cells in the spinal cord that process mechanical information and contribute to touch-evoked pain. Future studies will identify the nerve circuits that are targeted by CGRP released from these nerve cells. These circuits represent a new therapeutic target for managing chronic pain conditions related to nerve damage, specifically mechanical allodynia, which is the most common complaint of patients with chronic pain.

Lack of correlation between spinal microgliosis and long-term development of tactile hypersensitivity in two different sciatic nerve crush injury.

Microglia activation following peripheral nerve injury has been shown to contribute to central sensitization of the spinal cord for the development of neuropathic pain. In a recent study, we reported that the amount of nerve damage does not necessarily correlate with chronic pain development. Here we compared the response of spinal microglia, using immunohistochemistry as a surrogate of microglial activation, in mice with two different types of crush injury of the sciatic nerve. We confirmed that incomplete crush of the sciatic nerve (partial crush injury, PCI) resulted in tactile hypersensitivity after the recovery of sensory function (15 days after surgery), whereas the hypersensitivity was not observed after the complete crush (full crush injury, FCI). We observed that immunoreactivity for Iba-1, a microglial marker, was greater in the ipsilateral dorsal horn of lumbar (L4) spinal cord of mice 2 days after FCI compared to PCI, positively correlating with the intensity of crush injury. Ipsilateral Iba-1 reactivity was comparable between injuries at 7 days with a significant increase compared to the contralateral side. By day 15 after injury, ipsilateral Iba-1 immunoreactivity was much reduced compared to day 7 and was not different between the groups. Our results suggest that the magnitude of the early microgliosis is dependent on injury severity, but does not necessarily correlate with the long-term development of chronic pain-like hypersensitivity after peripheral nerve injury.

Impaired Limb Functional Outcome of Peripheral Nerve Regeneration Is Marked by Incomplete Recovery of Paw Muscle Atrophy and Brain Functional Connectivity in a Rat Forearm Nerve Repair Model.

Skilled sensorimotor deficit is an unsolved problem of peripheral nerve injury (PNI) led by limb trauma or malignancies, despite the improvements in surgical techniques of peripheral nerve anastomosis. It is now accepted that successful functional recovery of PNI relies tremendously on the multilevel neural plasticity from the muscle to the brain. However, animal models that recapitulate these processes are still lacking. In this report, we developed a rat model of PNI to longitudinally assess peripheral muscle reinnervation and brain functional reorganization using noninvasive imaging technology. Based on such model, we compared the longitudinal changes of the rat forepaw intrinsic muscle volume and the seed-based functional connectivity of the sensorimotor cortex after nerve repair. We found that the improvement of skilled limb function and the recovery of paw intrinsic muscle following nerve regeneration are incomplete, which correlated with the functional connectivity between the primary motor cortex and dorsal striatum. Our results were highly relevant to the clinical observations and provided a framework for future investigations that aim to study the peripheral central sensorimotor circuitry underlying skilled limb function recovery after PNI.

Macrophage roles in peripheral nervous system injury and pathology: Allies in neuromuscular junction recovery.

Peripheral nerve injuries remain challenging to treat despite extensive research on reparative processes at the injury site. Recent studies have emphasized the importance of immune cells, particularly macrophages, in recovery from nerve injury. Macrophage plasticity enables numerous functions at the injury site. At early time points, macrophages perform inflammatory functions, but at later time points, they adopt pro-regenerative phenotypes to support nerve regeneration. Research has largely been limited, however, to the injury site. The neuromuscular junction (NMJ), the synapse between the nerve terminal and end target muscle, has received comparatively less attention, despite the importance of NMJ reinnervation for motor recovery. Macrophages are present at the NMJ following nerve injury. Moreover, in denervating diseases, such as amyotrophic lateral sclerosis (ALS), macrophages may also play beneficial roles at the NMJ. Evidence of positive macrophages roles at the injury site after peripheral nerve injury and at the NMJ in denervating pathologies suggest that macrophages may promote NMJ reinnervation. In this review, we discuss the intersection of nerve injury and immunity, with a focus on macrophages.

Electrophysiological investigation of motor axonal excitability in a mouse model of nerve constriction injury.

Peripheral nerve injuries caused by focal constriction are characterised by local nerve ischaemia, axonal degeneration, demyelination, and neuroinflammation. The aim of this study was to understand temporal changes in the excitability properties of injured motor axons in a mouse model of nerve constriction injury (NCI). The excitability of motor axons following unilateral sciatic NCI was studied in male C57BL/6J mice distal to the site of injury at the acute (6 hours-1 week) and chronic (up to 20 weeks) phases of injury, using threshold tracking. Multiple measures of nerve excitability, including strength-duration properties, threshold electrotonus, current-threshold relationship, and recovery cycle were examined using the automated nerve excitability protocol (TRONDNF). Acutely, injured motor axons developed a pattern of excitability characteristic of ischemic depolarisation. In most cases, the sciatic nerve became transiently inexcitable. When a liminal compound muscle action potential could again be recorded, it had an increase in threshold and latency, compared to both pre-injury baseline and sham-injured groups. These axons showed a greater threshold change in response to hyperpolarising threshold electrotonus and a significant upward shift in the recovery cycle. Mathematical modelling suggested that the changes seen in chronically injured axons involve shortened internodes, reduced myelination, and exposed juxtaparanodal fast K+ conductances. The findings of this study demonstrate long-term changes in motor excitability following NCI (involving alterations in axonal properties and ion channel activity) and are important for understanding the mechanisms of neurapraxic injuries and traumatic mononeuropathies.

A subset of spinal dorsal horn interneurons crucial for gating touch-evoked pain-like behavior.

A cardinal, intractable symptom of neuropathic pain is mechanical allodynia, pain caused by innocuous stimuli via low-threshold mechanoreceptors such as Aß fibers. However, the mechanism by which Aß fiber-derived signals are converted to pain remains incompletely understood. Here we identify a subset of inhibitory interneurons in the spinal dorsal horn (SDH) operated by adeno-associated viral vectors incorporating a neuropeptide Y promoter (AAV-NpyP+) and show that specific ablation or silencing of AAV-NpyP+ SDH interneurons converted touch-sensing Aß fiber-derived signals to morphine-resistant pain-like behavioral responses. AAV-NpyP+ neurons received excitatory inputs from Aß fibers and transmitted inhibitory GABA signals to lamina I neurons projecting to the brain. In a model of neuropathic pain developed by peripheral nerve injury, AAV-NpyP+ neurons exhibited deeper resting membrane potentials, and their excitation by Aß fibers was impaired. Conversely, chemogenetic activation of AAV-NpyP+ neurons in nerve-injured rats reversed Aß fiber-derived neuropathic pain-like behavior that was shown to be morphine-resistant and reduced pathological neuronal activation of superficial SDH including lamina I. These findings suggest that identified inhibitory SDH interneurons that act as a critical brake on conversion of touch-sensing Aß fiber signals into pain-like behavioral responses. Thus, enhancing activity of these neurons may offer a novel strategy for treating neuropathic allodynia.

Positive Regulatory Domain I-binding Factor 1 Mediates Peripheral Nerve Injury-induced Nociception in Mice by Repressing Kv4.3 Channel Expression.

BACKGROUND: The transcriptional repressor positive regulatory domain I-binding factor 1 (PRDM1) is expressed in adult mouse dorsal root ganglion and regulates the formation and function of peripheral sensory neurons. The authors hypothesized that PRDM1 in the dorsal root ganglion may contribute to peripheral nerve injury-induced nociception regulation and that its mechanism may involve Kv4.3 channel transcriptional repression. METHODS: Nociception was induced in C57BL/6 mice by applying chronic constriction injury, complete Freund's adjuvant, or capsaicin plantar injection. Nociceptive response was evaluated by mechanical allodynia, thermal hyperalgesia, cold hyperalgesia, or gait analysis. The role of PRDM1 was evaluated by injection of Prdm1 knockdown and overexpression adeno-associated viruses. The interaction of PRDM1 at the Kv4.3 (Kcnd3) promoter was evaluated by chromatin immunoprecipitation assay. Excitability of dorsal root ganglion neurons was evaluated by whole cell patch clamp recordings, and calcium signaling in spinal dorsal horn neurons was evaluated by in vivo two-photon imaging. RESULTS: Peripheral nerve injury increased PRDM1 expression in the dorsal root ganglion, which reduced the activity of the Kv4.3 promoter and repressed Kv4.3 channel expression (injured vs. uninjured; all P < 0.001). Knockdown of PRDM1 rescued Kv4.3 expression, reduced the high excitability of injured dorsal root ganglion neurons, and alleviated peripheral nerve injury-induced nociception (short hairpin RNA vs. Scram; all P < 0.05). In contrast, PRDM1 overexpression in naive mouse dorsal root ganglion neurons diminished Kv4.3 channel expression and induced hyperalgesia (PRDM1 overexpression vs. control, mean ± SD; n = 13; all P < 0.0001) as evaluated by mechanical allodynia (0.6 ± 0.3 vs. 1.2 ± 0.2 g), thermal hyperalgesia (5.2 ± 1.3 vs. 9.8 ± 1.7 s), and cold hyperalgesia (3.4 ± 0.5 vs. 5.3 ± 0.6 s). Finally, PRDM1 downregulation in naive mice reduced the calcium signaling response of spinal dorsal horn neurons to thermal stimulation. CONCLUSIONS: PRDM1 contributes to peripheral nerve injury-induced nociception by repressing Kv4.3 channel expression in injured dorsal root ganglion neurons.

Assessments of regenerative potential of silymarin nanoparticles loaded into chitosan conduit on peripheral nerve regeneration: a transected sciatic nerve model in rat.

PURPOSE: It is compulsory to make a tension-free, end-to-end repair in transected injuries. However, when it comes to longer defects, placement of an autograft or nerve conduits is required. The present study was designed to assess regenerative potential of silymarin nanoparticles loaded into chitosan conduit on peripheral nerve regeneration in a transected sciatic nerve model in rat. METHODS: In NML group left sciatic nerve was exposed through a gluteal muscle incision and after careful hemostasis skin was closed. In TSC group left sciatic nerve was transected and stumps were fixed in adjacent muscle. In CTN group, 10-mm sciatic nerve defects were bridged using a chitosan. In CTN/NSLM group, 10-mm sciatic nerve defects were bridged using a chitosan conduit and 100 µL silymarin nanoparticles were administered into the conduit. The regenerated fibers were studied 4, 8, and 12 weeks after surgery. Assessment of nerve regeneration was based on behavioral, functional, biomechanical, histomorphometric, and immuohistochemical criteria. RESULTS: The behavioral, functional, electrophysiological, and biomechanical studies confirmed significant recovery of regenerated axons in CTN/NSLM group (P < 0.05). Quantitative morphometric analyses of regenerated fibers showed number and diameter of myelinated fibers in CTN/NSLM group were significantly higher than in CTN group (P < 0.05). DISCUSSION: This demonstrated potential of using chitosan-silymarin nanoparticles in peripheral nerve regeneration without limitations of donor-site morbidity associated with isolation of autograft. It is also cost saving and may have clinical implications for surgical management of patients after peripheral nerve transection.

N-acetylcysteine maintains penile length and erectile function in bilateral cavernous nerve crush rat model by reducing penile fibrosis.

Penile length shortening and erectile dysfunction are common complications after radical prostatectomy. Various methods have been used to maintain erectile function, but less attention has been paid to preserving penis length. N-acetylcysteine (NAC) has the effect of antioxidation and antifibrotic, which may be beneficial to improve those postoperative complications. This study investigated the effect of NAC on maintaining the penile length and the erectile function after bilateral cavernous nerve crush (BCNC) and its underlying mechanism. Twenty-four male rats were randomly divided into three groups: control group, BCNC group, and BCNC + NAC group. NAC or equal volume of saline was daily administrated by intragastric gavage for 4 weeks. The initial and end penile lengths were measured. Intracavernosal pressure/mean arterial pressure (ICP/MAP) ratio was calculated to assess erectile function. Hematoxylin-eosin staining, Masson's trichrome staining, immunohistochemistry, and Western blot were performed to explore cellular and molecular changes of the penis. Compared to the BCNC group, the penile length, ICP/MAP ratio and smooth muscle/collagen ratio in the BCNC + NAC group were improved significantly (all P < 0.05), and the expressions of endothelial nitric oxide synthase, α-smooth muscle actin, glutathione, and glutathione peroxidase 1 were significantly increased after NAC treated (all P < 0.05), along with the decreased expressions of hypoxia-inducible factor-1α, transforming growth factor-ß1, collagen I, collagen III, collagen IV, malonaldehyde, and lysine oxidase (all P < 0.05). This study demonstrated that NAC could maintain penile length and partly improve erectile function. Possible mechanism is directly and/or indirectly related to antihypoxic and antifibrosis.